1. Field of the Invention
This invention relates to an improved method and an improved apparatus for the continuous treatment of waste wood, such as stumps and snag, to make it suitable for the production of paper pulp, whereby the incoming wood material is initially crushed in order to detach part of the impurities therein and the crushed material is substantially washed with water in a washer tank.
2. Description of the Prior Art
As it is becoming more difficult to obtain wood for cellulose production and as wood prices are on the increase, more attention is being paid to the possibilities of exploiting waste wood. Thus, stumps and snag will play a substantial role as raw material.
Although the strength properties of cellulose manufactured from conventional wood chips are somewhat better than those of cellulose pulp produced from waste wood, small and even considerable quantities of stump material mixed with other wood material will not substantially affect the quality of the produced paper. For example, in sack paper a small portion of stump material is even advantageous as it improves the formation.
The limitatiOns of using marginal wood are not so much due to its fiber properties as they are to the difficulties and expenses caused by the impurities present in it. These impurities mainly consist of stones, sand, and earth; bark can also be counted among them. The separation of the impurities is often complicated by the fact that they are partly imbedded in the wood. Furthermore, it is obviously more difficult to remove bark from stumps than from ordinary paper timber, owing to the irregular shapes of stumps.
Mainly because of the above problems, the conclusion made in research so far has generally been that the use of waste wood for pulp production is in principle possible but in practice too uneconomical to implement.